Typical optical networks are based on high-speed electronic routers interconnected by optical fiber links utilizing wavelength division multiplexing (WDM) transmission systems. To achieve packet routing, the optical signal entering the router is converted to an electrical signal (O/E conversion) and demultiplexed into lower-rate data streams. The data streams are electronically routed and multiplexed in a high-speed electrical signal that is generated by the router for a specific optical wavelength.
As the demand for bandwidth in optical networks continues to increase, the router must be able to perform its switching at higher rates. The electronic signal bandwidth limitations incurred during the O/E conversion and the conversion back to an optical signal (E/O conversion), however, often result in router congestion and reduced data throughput. In addition, the low energy optical pulses received at the router after propagation over long distances can be degraded, for example, by chromatic dispersion and nonlinear effects in the transmission fiber. The optical pulses can also exhibit timing variations (i.e., jitter) within a bit interval.
Conventional electronic signal regenerators provide pulse amplification, pulse shaping and timing jitter correction of an electrical signal. For WDM networks, an electronic signal regenerator is required for each wavelength channel. After the O/E conversion, the single wavelength channel electronic data is demultiplexed into lower-rate data streams and each stream is processed electronically. The lower-rate data streams are multiplexed into a single data stream that is used to modulate the desired wavelength optical carrier. The use of electronic regenerators for re-amplification, re-shaping and re-timing in high-speed optical networks is often prohibited by cost, complexity, and power in many-channel WDM networks and sometimes is limited by processing speed in ultrafast optical time domain multiplexing (OTDM) networks.
All-optical switches eliminate the need for the O/E conversion and E/O conversion. Consequently, all-optical switches generally support higher data rates than electronic switches. Optical switches utilizing nonlinearities in optical fibers are subject to polarization instability due to temperature variations and acoustic disturbances. Semiconductor materials are used as the nonlinear media in some optical switches, however, the operational speed of these switches is typically limited by multiple physical processes. For example, long-lasting refractive index nonlinearities cause performance degradations that are dependent on the data statistics and the data rate.